CELLULOSE ESTER BASED MEMBRANES FOR OSMOTIC PROCESSES ONG RUI CHIN NATIONAL UNIVERSITY OF SINGAPORE 2014 CELLULOSE ESTER BASED MEMBRANES FOR OSMOTIC PROCESSES ONG RUI CHIN (B. Eng.) National University of Singapore A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2014 Declaration I hereby declare that the thesis is my original work and it has been written by me in its entirety. I have duly acknowledged all the sources of information which have been used in the thesis. This thesis has also not been submitted for any degree in any university previously. ____________________________ Ong Rui Chin March 2014 i ACKNOWLEDGEMENT First of all, I would like to extend my utmost gratitude and appreciation to my supervisor, Professor Chung Tai-Shung from the Department of Chemical and Biomolecular Engineering, National University of Singapore (NUS). His continuous encouragement, patience and guidance have been the very essential throughout my PhD journey. He is never hesitant in sharing knowledge and always inspires me with his enthusiasm and passion towards membrane research. I would also like to sincerely thank my PhD thesis advisory committee members, Professor Ting Yen Peng and Professor Chen Shing Bor for their valuable suggestions on the areas for improvement throughout my candidature in NUS. I would also like to thank Professor Donald R. Paul, for sharing his professional knowledge on the fundamental polymer science and membrane transport. Thanks are also due to Professor Y. C. Jean and Dr. H. Chen for sharing their knowledge in PALS analyses for polymeric membranes which are very essential in most of my work. I would like express my gratitude towards Eastman Chemical Company for the research funding through the project titled “Investigation of Novel Materials for the Forward Osmosis Process” (grant number R-279-000-315-597) and synthesizing the cellulose esters which are the core of my PhD work. Special thanks are due to Dr. Bradley Helmer and Dr. Jos de Wit for their kind advice in my research work. Thanks are also due to the Singapore National Research Foundation (NRF) (grant number R-279-000-336-281 and R-279-000-339-281) for the financial support. ii I would also like to convey my personal appreciation to all former and current members of our membrane research group, especially Dr. Wang Kaiyu, Dr. Teoh May May, Dr. Wang Yan, Dr. Zhang Sui, Dr. Li Xue and Dr. Natalia Widjojo for sharing their valuable knowledge without any reservation. Special thanks are due to Ms. Zhong Peishan and Ms. Fu Xiu Zhu for their valuable comments on my PhD dissertation. I would also like to thank Ms. Nguyen Thi Mai Thao, Ms. Li Xiaoman, Mr. Khoo Yong Seng, Tony, Ms. Liang Jiayue and Ms. Lin Xiaochen for the assistance given to me. My sincere thanks are due to all staff members in the Department of Chemical and Biomolecular Engineering, especially Mr. Ng Kim Poi, Mr. Chia Pai Ann and Mr. Liu Zhicheng. My gratitude is also extended to Mr. Lim Poh Chong at Institute of Material Research and Engineering (IMRE) for his help on XRD analysis. Last but not least, I would like to thank my parents, sisters and husband for their unconditional love and support. iii TABLE OF CONTENTS ACKNOWLEDGEMENT ii TABLE OF CONTENTS iv SUMMARY ix LIST OF TABLES . xiv LIST OF FIGURES . xvi NOMENCLATURE . xxi Chapter Introduction . 1.1 An Overview of Osmosis and Osmotic Pressure 1.2 Classifications of Osmotic Processes . 1.3 The Development and Applications of Forward Osmosis . 1.3.1 Desalination . 1.3.2 Liquid food concentration and pharmaceutical applications . 1.3.3 Other applications 1.4 Challenges in Forward Osmosis 11 1.4.1 Concentration polarization . 11 1.4.2 Reverse solute diffusion . 13 1.4.3 Development of draw solutes . 14 1.5 Membranes for Forward Osmosis . 18 1.5.1 Asymmetric membranes with integrally-grown selective layer by phase inversion . 21 1.5.2 Composite membranes . 25 iv 1.6 Cellulose Esters . 34 1.7 Mass Transport in Forward Osmosis . 37 1.7.1 External concentration polarization . 38 1.7.2 Internal concentration polarization 40 1.7.3 Solute reverse flux . 43 1.8 Research Objectives and Thesis Organization . 43 Chapter Formation of Cellulose Triacetate Forward Osmosis Membranes 47 2.1 Introduction . 47 2.2 Experimental . 48 2.2.1 Materials 48 2.2.2 Membrane fabrication 49 2.2.3 Positron annihilation lifetime spectroscopy (PALS) . 50 2.2.4 Molecular simulations by Material Studio . 51 2.2.5 Fourier transform infrared spectroscopy (FTIR) analysis . 52 2.2.6 Mean pore size and pore size distribution 52 2.2.7 Forward osmosis tests and salt rejection tests 53 2.3 Results and Discussion 55 2.3.1 Morphology of CTA membranes . 55 2.3.2 Membrane morphology characterized by PAS 57 2.3.3 Effects on solvent systems on the CTA membrane morphology . 62 2.3.4 Mean pore size and pore size distribution 69 2.4 Conclusions 77 Chapter Novel Cellulose Esters for Forward Osmosis Membranes . 79 v 3.1 Introduction . 79 3.2 Experimental . 82 3.2.1 Materials 82 3.2.2 Membrane preparation . 85 3.2.3 Morphological studies 86 3.2.4 Fractional free volume calculations and density determination 86 3.2.5 Pure water permeability, salt rejection and salt permeability tests 87 3.2.6 Forward osmosis tests 87 3.3 Results and Discussion 88 3.3.1 Viscosity curves and critical concentration evaluation 88 3.3.2 Membrane morphology 90 3.3.3 Performance of cellulose ester membranes 94 3.3.4 Effects of DS and functional group on membranes’ FO performance 97 3.3.5 FO performance of CAB_M membranes at different draw solution concentrations . 105 3.4 Conclusion . 107 Chapter Free Volume, Fundamental Water and Salt transport Properties of Novel Cellulose Esters and Their Relationships to the Functional Groups . 108 4.1 Introduction . 108 4.2. Experimental 111 4.2.1. Chemicals 111 4.2.2 Dense film preparation . 112 4.2.3 Positron annihilation lifetime spectroscopy (PALS) . 113 4.2.4 Equilibrium water uptake and salt partition coefficient measurements . 115 vi 4.2.5 Pure water and salt permeability measurements 116 4.2.6 Water and salt diffusivity . 117 4.2.7 Water/salt selectivity 117 4.3 Results and discussion 118 4.3.1 Free volumes of cellulose ester films . 118 4.3.2 Equilibrium water uptake, salt partition coefficient, Ks and solubility parameters . 122 4.3.3 Permeability and diffusivity characteristics of various cellulose esters 126 4.3.4 Solubility selectivity, αK, and diffusivity selectivity, αD . 128 4.4 Conclusions 132 Chapter Novel Hydrophilic Cellulose Ester Supported Thin Film Composite Forward Osmosis Membranes . 133 5.1 Introduction . 133 5.2 Materials and Methods . 135 5.2.1 Fabrication of cellulose ester membrane supports . 135 5.2.2 Interfacial polymerization and post-treatment methods of flatsheet TFC-FO membranes 137 5.2.3 Characterizations of cellulose ester membrane supports and TFC-FO membranes 138 5.2.4 Forward osmosis tests 139 5.2.5 Determination of transport and structural parameters . 139 5.3 Results and Discussion 140 5.3.1 Characteristics of cellulose ester membrane supports . 140 5.3.2 Characteristics of TFC-FO membranes subjected to various post-treatment methods . 143 vii 5.3.3 Forward osmosis performance of TFC-FO membranes 144 5.3.4 PALS analyses . 147 5.3.5 Seawater desalination . 148 5.3.6 Performance comparisons with existing TFC-FO membranes reported in literatures . 150 5.4 Conclusions 152 Chapter Conclusions 153 REFERENCES 155 A LIST OF JOURNAL PUBLICATIONS . 182 viii [114] J. 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Han, Emerging forward osmosis (FO) technologies and challenges ahead for clean water and clean energy applications, Current Opinion in Chemical Engineering, (2012) 246-257. 182 [...]... especially for seawater desalination due to the high osmotic pressure of seawater In this chapter, the osmotic processes and the invention of various membranes for these processes will be introduced In addition, an overview of cellulose esters as materials for osmotic membranes will also be summarized in this chapter 1.2 Classifications of Osmotic Processes The concept of osmotic processes for water... this work, a hydrophilic cellulose ester with a high intrinsic water permeability and a water partition coefficient was chosen to fabricate highly porous membrane supports for flat-sheet thin film composite FO (TFC-FO) membranes The polyamide selective layer is formed by interfacial polymerization The performance of TFC-FO membranes prepared from the hydrophilic cellulose ester groups clearly surpasses... decades ago [8-12] In osmotic processes, membranes serve as the core that enables the separation of water from solution mixtures by the rejection of solutes Membrane based osmotic processes can be categorized into three categories: (1) Reverse Osmosis (RO), (2) Forward Osmosis (FO), and (3) Pressure Retarded Osmosis (PRO) Among these processes, RO and FO are studied extensively for their applications... permeation Highly hydrophobic cellulose esters are unable to form selective layers without defects under normal casting conditions due to rapid phase inversion For further understanding on the fundamental properties of various cellulose esters, transport properties including salt and water partition coefficients, permeability and diffusivity of various newly synthesized cellulose esters were evaluated in... butyryl (Bu) functional groups of cellulose esters used in this study 83 Table 3.2 Critical concentrations of cellulose esters in NMP and compositions of casting solutions 89 Table 3.3 Pure water permeability, A (LMH bar-1), salt permeability, B (LMH), salt rejection, Rs at 10 bar 94 Table 3.4 FO performance of cellulose ester membranes 96 xiv Table 3.5... PWP of Cellulose Ester Membrane Supports 141 Table 5.2 PRO and FO Performance of TFC-FO Membranes using 1.0 M NaCl Draw Solution 144 Table 5.3 The transport parameters A, B and the structural parameter S of TFC-O-II membranes, calculated by the Excel -based error minimization algorithm developed by Tiraferri et al [233] The related coefficients of determination, R2 for both... indicates bottom layer facing draw solution 76 xvii Figure 3.1 Map of design strategy for novel cellulose esters as a function of hydrophilic DS(OH) vs the ratio of hydrophobic DS(Pr) for CAP or DS(Bu) for CAB to the total DS of bulky side groups 84 Figure 3.2 Viscosity curves of cellulose esters as a function of polymer concentration 88 in NMP solutions at a shear rate of 10... (MWCO) of CTA membranes 70 Table 2.6 FO performance of CTA membranes before annealing Draw solution: 2M NaCl, feed: DI water 72 Table 2.7 FO performance of CTA membranes after annealing Both top layer faces draw solution (DS) and bottom layer faces DS orientations were tested Draw solution: 2M NaCl, feed: DI water 74 Table 2.8 Annealed CTA membranes rejections... that leads to significant differences in the as-cast membrane morphology x Subsequently, a wide range of cellulose esters were newly synthesized and studied for their potential as FO membrane materials Synthesis and evaluation of novel cellulose esters with a range of chemical compositions targeted for forward osmosis (FO) membrane fabrication have been carried out Preliminary studies on the effects of... recently for its potential to harvest energy over the salinity gradient between fresh and sea water Among these osmotic processes, FO for water separations will be the subject of interest for this dissertation This is due to the fact that the current state-of-art RO membranes and process have achieved a matured state where the energy consumption is approaching the theoretical minimum [13] Whereas for FO, . CELLULOSE ESTER BASED MEMBRANES FOR OSMOTIC PROCESSES ONG RUI CHIN NATIONAL UNIVERSITY OF SINGAPORE 2014 CELLULOSE ESTER BASED MEMBRANES FOR OSMOTIC PROCESSES. Characteristics of cellulose ester membrane supports 140 5.3.2 Characteristics of TFC-FO membranes subjected to various post-treatment methods 143 viii 5.3.3 Forward osmosis performance of TFC-FO membranes. cut off (MWCO) of CTA membranes 70 Table 2.6 FO performance of CTA membranes before annealing. Draw solution: 2M NaCl, feed: DI water. 72 Table 2.7 FO performance of CTA membranes after annealing.